-LRB- CNN -RRB- -- Tribal fighters took control of a top Yemeni city on Tuesday , a setback for an embattled government whose wounded president is hospitalized in Saudi Arabia .

More than 400 tribal gunmen took over Taiz in southwest Yemen , witnesses there said .

Government forces have been regrouping in an effort to re-enter the city . Yemen 's government has faced international criticism for excessive use of force against anti-regime protesters and the deaths of anti-government demonstrators in Taiz .

Are you in Yemen ? Share your photos and videos from the scene , but please stay safe .

Meanwhile , President Ali Abdullah Saleh was in Saudi Arabia Tuesday , recovering from burns over 40 % of his body and a collapsed lung , a U.S. government official briefed on the matter said .

Whether he will return to Yemen remained uncertain .

Saleh was wounded Friday in an attack at his presidential compound . An Arab diplomatic source with knowledge of Saleh 's condition said one shrapnel wound was 7 centimeters -LRB- 2.75 inches -RRB- deep .

Fighting between government and tribal forces has been raging in the capital of Sanaa , where thousands of anti-government protesters have been pressuring Saleh to give up power since January . And there has been unrest elsewhere .

At least 15 people were killed in Abyan Monday night and Tuesday morning in clashes between Islamic militants and security forces , according to a security source in Abyan .

Al Qaeda in the Arabian Peninsula has a presence in the southern province of Abyan , a U.S. official said . It 's also home to an Islamic militant movement that has targeted government troops in recent days .

The Abyan dead include nine soldiers , four militants and two civilians in Zinjibar and other suburbs in the province , according to the source , who asked to not be named because he is not authorized to speak to the media .

There was also violence along the Saudi-Yemeni border , where there have long been concerns of infiltration by militants .

A man trying to cross into Yemen from Saudi Arabia early Tuesday fatally shot two security officers and wounded another , the state-run Saudi Press Agency said Tuesday .

The man , described as an `` infiltrator '' who tried to cross the metal-and-sand barriers at the border , fired at the security officers when they approached him , the agency said . Security personnel tracked the man and he was killed in an exchange of fire , it added .

The turmoil in Yemen peaked Friday , when a mosque in Saleh 's presidential compound was attacked . Yemen 's state-run news agency SABA , citing a source in Saleh 's office , reported last week that three guards and an imam were killed .

Western diplomats said the attack came from a bomb . Yemeni investigations are `` focusing on what happened inside the mosque , '' not a rocket or mortar attack , diplomats said Monday . One diplomat said the attack was not a suicide bombing and that the Yemeni investigation was ongoing .

The description of the attack as a bombing differs from what a Yemeni official told CNN last week . The official , who asked not to be identified , said that Saleh was in the mosque when two `` projectiles '' were fired during Friday prayers .

Supporters of Sadeq Al-Ahmar , leader of the Hashed tribe and an opponent of the Yemeni government , were suspected in the attack .

In response , Yemeni security forces shelled Al-Ahmar 's home Friday , killing 10 people and wounding 35 others , according to Fawzi Al-Jaradi , an official with the Hashed tribal confederation .

After Saleh was taken to Saudi Arabia for treatment , the tribal leader and Vice President Abed Rabbo Mansour Hadi -- Yemen 's interim leader -- agreed on a cease-fire , said Abdulqawi Al-Qaisi , spokesman for the Hashed leader .

Yemen 's largest opposition bloc has vowed to prevent Saleh from returning .

`` The Yemeni people will do all in their power to not allow Saleh to re-enter the country , '' Joint Meeting Parties spokesman Mohammed Qahtan said Sunday .

A U.S. government official said Monday he could not imagine the Saudis letting Saleh return . He said it was critical that the Saudis press Saleh to accept a Gulf Cooperation Council deal offering him immunity in exchange for stepping down .

Saudi state-run Ekhbariya television reported Monday that Saleh had undergone two operations in Saudi Arabia and would return to Yemen after he recovers .

A U.S. official told CNN Monday that the unrest makes U.S. counterterrorism efforts in Yemen `` more difficult . ''

`` We rely on the Yemeni government as partners , '' the official said . `` The more the government is distracted by the political unrest , the more difficult it is for us . ''

The Yemeni government has had a `` big impact on acquiring information on AQAP , '' the official said , referring to al Qaeda in the Arabian Peninsula . `` If that information flow slows or stops , it inhibits our ability to gather information . ''

CNN 's Nic Robertson , Elise Labott , Pam Benson , Tim Lister and Jill Dougherty contributed to this report .

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After rebel gunmen take over Taiz , witnesses say , government forces try to regroup

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Saleh is in Saudi Arabia for treatment after being wounded

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A U.S. official says the unrest in Yemen makes counterterrorism efforts `` more difficult ''